Evaluation of Image Quality Change by Truncated Region in Brain PET/CT

Objectives The purpose of this study was to evaluate image quality change by truncated region in field of view(FOV) of attenuation correction computed tomography(AC-CT) in brain PET/CT.

Methods Biograph Truepoint 40 with TrueV(Siemens) was used as a scanner. ⁶⁸Ge phantom scan was performed with and without applying brain holder using brain PET/CT protocol. PET attenuation correction factor(ACF) was evaluated according to existence of pallet in FOV of AC-CT. FBP, OSEM3D and PSF methods were applied for PET reconstruction. Parameters of iteration 4, subsets 21 and gaussian 2mm filter were applied for iterative reconstruction methods. Window level 2,900, width 6,000 and level 4,200, width 1,000 were set for visual evaluation of PET AC images. Vertical profiles of 5 slices and 20 slices summation images applied gaussian 5mm filter were produced for evaluating integral uniformity.

Results Patient pallet was not covered in FOV of AC-CT when without applying brain holder because of small size of FOV. It resulted in defect of ACF sinogram by truncated region in ACF evaluation. When without applying brain holder, defect was appeared in lower part of transverse image on condition of window level 4,200, width 1,000 in PET AC image evaluation. With and without applying brain holder, integral uniformities of 5 slices and 20 slices summation images were 7.2%, 6.7% and 11.7%, 6.7%.

Conclusions Truncated region by small FOV results in count defect in occipital lobe of brain in clinical or research studies. It is necessary to understand effect of truncated region and apply appropriate accessory for brain PET/CT.